Occupations such as firefighting and police work often require personnel to perform under extreme physical and mental stress. Real time physiological monitoring of such personnel can be a useful tool for recognizing when personnel are in danger of exceeding their physical limits. Physiological parameters such as heart rate, heart rate variability (HRV) and respiration provide early warning signs of high stress that can be used to protect health and safety. However, existing devices for measuring such parameters are generally bulky, uncomfortable to wear, and not effective for occupational monitoring.
A government study on firefighter fatality showed that 50% of firefighter deaths are caused by heart attacks. Thus, monitoring a firefighter's vital signs during and after high-stress missions can assist in preventing heart attacks or in providing immediate medical attention when it is determined that a firefighter is close to having a heart attack. Further, police officers are known to have over twice the incidence of cardiovascular disease as the general population. A study determined that being employed in law enforcement places one at a greater risk of developing cardiovascular disease than having high blood pressure, having diabetes, being overweight, or being a smoker. Unlike firefighters, whose heart rates increase mainly from physical stress, in police officers unhealthy heart rate increases are often due to emotional stress. Nevertheless, as in the case of firefighters, heart rate monitoring of police officers can also improve health and safety. For example, a command center can be alerted when an officer has been exposed to a high stress situation for too long. Real time physiological monitoring of police and firefighter personnel can also assist in training and self-evaluation.
Among the most important vital signs that can indicate impending heart attacks are heart rate and HRV. Changes in beat-to-beat heart rate determine HRV. In general, a higher HRV is desirable; lower HRV has been found to be a significant predictor of cardiac mortality and morbidity. By evaluating HRV it is often possible to assess a person's heart performance and the onset of a heart malfunction.
An effective real time physiological monitoring system for high stress occupational environments must satisfy numerous criteria. It must be comfortable to wear, low-weight, passive, and robust. Preferably, such a system should also conform well to a person's existing clothing and equipment.
Auscultation is a class of methods used to listen to the sounds of the body during a physical examination and is widely recognized as an important diagnostic tool. Auscultation is most commonly performed by listening through a stethoscope, where a medical professional may auscultate a patient's lungs, heart, and intestines to evaluate the frequency, intensity, duration, number, or quality of sounds. But generally such procedures are performed in a controlled and quiet environment such as in a clinic or hospital. Standard stethoscopes are thus not designed for and are not effective at monitoring heart and respiratory parameters over extended periods in harsh occupational environments.
Prior art devices for measuring heart rate and respiration, including stethoscopes, generally require direct contact with the skin. Other common physiological sensors include electrodes or small microphones that are adhered directly to the skin with tape or wrappings. Electrodes measure the electrical impulses associated with physiological parameters; whereas microphones detect the sound of organs such as the heart and lungs. Wires leading from these sensors are then generally connected to some form of data acquisition device or data transceiver. Disadvantages of these devices include the fact that they require additional time and effort to attach to the body. Such time requirements can be particularly problematic for emergency response personnel who already are required to outfit themselves with sophisticated equipment, such as breathing apparatuses, in very limited time periods. Further, wiring from such prior art devices can be uncomfortable and can impede movement.